Several types of spiral exchangers exist in the state of the art. Typically, such exchangers are formed by two superimposed sheets that are then wound and arranged in an exhaust duct of an internal combustion engine.
In one type of spiral exchanger, the sheets are spaced apart with spacers. For example, application FR 2 810 726 A1 discloses a spiral exchanger that is made by two sheets spaced apart that have, on their surfaces across from the inner spacing elements and the opposite surface, respectively, outer spacing elements that are arranged so that the inner and outer spacing elements of one sheet bear on the corresponding inner and outer spacing elements of the other sheet. The spacing elements have substantially the same shape. In application FR 2 809 483 A1, a metal strip having spacing elements is formed by folding the edges, which are then connected to one another by welding. The folded metal strip is then wound to form the spiral exchanger.
Application FR 2 874 080 A1 relates to an exchanger comprising two wound metal sheets. The metal sheets are provided with spacing elements in the form of serrations distributed on the surface thereof. Furthermore, the inlet and outlet for the fluid, for example water, of the device are done at a center of the spiral. This means that the inlet and outlet tubes will exit on either side of the exchanger and have a complicated trajectory, which is therefore costly. Typically, the water circulating in such an exchanger is at most at a temperature of 130° C., and therefore significantly below that of the exhaust gas that heats the water. The fact that there are differential expansions between these water tubes and exhaust tubes may cause wear of the materials after extended use.
Generally, when two metal sheets are wound on one another, the metal sheet on the outer side is always longer than the inner sheet for an equivalent number of winding turns due to its thickness and/or the space between the two metal sheets. If the two metal sheets are welded before winding, for example as in application FR 2 809 483 A1, deformations will appear on the inner sheet. As a result, in the prior art, the sheets are often welded during or after winding, for example such as in application FR 2 810 726 A1. Nevertheless, welding during winding poses manufacturing problems, in particular for thin sheets. In fact, thin sheets cannot be welded using an electric arc and it is not possible to consider seam welding due to problems of accessing the heel that returns current. Furthermore, laser welding is difficult. The welding problem becomes increasingly complicated if it is necessary to perform intermediate welds between two side welds.
The aim of the present invention is to overcome the drawbacks of the state of the art and in particular to use a spiral exchanger that is easy to manufacture, light, and inexpensive.